RAID 5 vs RAID 6: The Data Loss Risk You Are Actually Taking

RAID protects against a drive dying, not against ransomware, accidental deletion, or a failed rebuild. Understanding the difference between RAID 5 and RAID 6 helps you choose the right level of safety for your data.

How RAID 5 works

RAID 5 spreads data and a single parity block across all drives in the array. It survives the failure of exactly one drive. Lose a second drive before the array is rebuilt, and the data is gone.

How RAID 6 works

RAID 6 stores two independent parity blocks, so it survives two simultaneous drive failures. That extra safety costs you one more drive worth of capacity and can slow writes slightly.

The rebuild problem

Here is the risk most people miss. When a drive fails, the array rebuilds by reading every remaining drive at full speed for hours or even days. On large arrays, that stress often pushes a second aging drive over the edge. On a RAID 5 array, that second failure means total loss. On RAID 6, you still have a safety net.

You still need a real backup

No RAID level is a substitute for a backup. RAID keeps you running through a hardware failure; a backup keeps you running through everything else. Pair your array with an off-site backup.

If an array has already failed

Never force a rebuild on a degraded or partially failed RAID without a full image of every member drive first. A wrong rebuild can overwrite the parity a recovery lab needs.